In a radio communication system, by sending control signaling, a control signaling transmitter notifies the control signaling receiver (terminal) of the information on the physical resources and transmission format for transmitting data. The control signaling receiver uses such information to receive downlink transmitted data or send uplink transmitted data. For example, in a Time Division Duplex (TDD) and/or Frequency Division Duplex (FDD) system, the control signaling transmitter needs to notify the timeslot and/or frequency used for transmitting data and other relevant information.
The transmission of control signaling in a system based on the Hybrid Automatic Repeat reQuest (HARQ) is described below as an example. The HARQ is a mechanism associated with packet retransmission between the data transmitter and the data receiver. If the data transmitter is a base station, the data receiver is a terminal. If the data transmitter is a terminal, the data receiver is a base station. By taking downlink adaptive HARQ as an example, the transmission of control signaling is described below, where the transmitter is a base station and the receiver is a terminal.
The base station notifies the terminal of allocated physical resources and HARQ-related information through downlink control signaling, and transmits the downlink data to the terminal. The control signaling may include time frequency resource, modulation mode, payload size, HARQ process number, Redundancy Version (RV), and New Data Indicator (NDI).
If the control signaling received by the terminal is erroneous, Discontinuous Transmission (DTX) is executed, namely, a DTX message is returned to the base station. Upon detecting the DTX fed back by the terminal, the base station sends downlink control signaling again and transmits packets.
If the control signaling received by the terminal is correct, the terminal receives packets as indicated by the control signaling. After receiving the packets correctly, the terminal returns a success acknowledgement (ACK) message to the base station, indicating that the current packet is received correctly. Subsequently, the base station sends the control signaling corresponding to the next packet, and sends the next packet. If the terminal fails to receive the packet correctly, the terminal returns a packet transmission failure acknowledgement, namely, Negative ACKnowledgement (NACK) message, to the base station, and the base station retransmits the control signaling and the packet which is not received by the terminal correctly.
The data transmitter can retransmit the packet for a limited number of times. If a packet is retransmitted for a threshold number of times but is still not received by the receiver successfully, the packet is referred to the upper layer.
In the foregoing process, for every attempt of transmitting the packet from the base station, no matter whether it is initial transmission or retransmission, the base station notifies the terminal through downlink control signaling.
The sent control signaling includes the fields such as physical resource indication, NDI, payload size, and RV. When a new packet is transmitted initially, the NDI value is different from that on the previous occasion. Specifically, if the value range of the NDI is 0 or 1, the NDI changes from 0 to 1, or from 1 to 0, when a new packet is transmitted initially. The value of RV is generally the default value in the initial transmission. If the packet is retransmitted, the NDI value is the same as that in the previous transmission, and the RV value changes. In this example, the RV is marked RV1 when the packet is retransmitted for the first time, marked RV2 when the packet is retransmitted for the second time, marked RV3 when the packet is retransmitted for the third time, marked RV4 when the packet is retransmitted for the fourth time, and so on. In the initial transmission and retransmission of the same packet, the payload size is the same. That is, the payload size needs to be indicated only in the initial transmission.
FIG. 1 is an exemplary signaling flow in a downlink adaptive HARQ process. As shown in FIG. 1, the process is as follows:
Step 101: The base station sends control signaling corresponding to the packet, and sends the packet initially (illustrated by dotted line 101 in FIG. 1), supposing that the control signaling indication NDI=0. The value of the payload size and the value of RV are indicated, and RV may adopt the default value.
Step 102: The terminal returns DTX. In this step, the terminal fails to receive the control signaling, and therefore, returns a DTX.
Step 103: The base station sends the control signaling again, and sends the packet initially (as illustrated by dotted line 103 in FIG. 1), where the value of NDI, the value of payload size, and the value of RV are the same as on the previous occasion, and the value of RV is the default value.
Step 104: The terminal returns a NACK message to the base station. In this step, the terminal receives the control signaling successfully, and therefore, the terminal receives the packet as indicated by the control signaling. If the terminal fails to receive the initially transmitted packet, the terminal returns a NACK to the base station.
Step 105: The base station sends control signaling corresponding to the retransmitted packet, and retransmits the packet (illustrated by dotted line 105 in FIG. 1). In this step, the packet is retransmitted for the first time. Therefore, in the control signaling, NDI=0, the value of the payload size is the same as that in the initial transmission, and the RV value is RV1 which is different from that on the previous occasion.
Afterwards, if the terminal still fails to receive the packet correctly, the base station keeps retransmitting the control signaling and the corresponding packet (as illustrated by step 106 and dotted line 106 in FIG. 1) until the threshold count of retransmission is reached. In the control signaling of retransmission, value of payload size is the same, and the RV changes. If the terminal still fails to receive the packet when the threshold count of retransmission is reached, the packet is referred to the upper layer.
Further, the base station sends control signaling of the new packet, and transmits the new packet. As shown in step 107 and dotted line 107, where the NDI in the control signaling is NDI=1 which is different from the NDI of the previous packet, the control signaling indicates the value of the payload size and the value of RV, and the value of the RV is the default value.
It is necessary to point out that the foregoing base station is a transmitter of the packet, and the terminal is a receiver of the packet. However, in the case of uplink data transmission, the data transmitter is a terminal, and the data receiver is a base station.
In the foregoing process, in the initial transmission of the packet, the RV in the corresponding control signaling may be a default value. The default value may not be indicated in the control signaling. Moreover, if the control signaling transmitted initially is received by the receiver successfully, namely, the receiver obtains the payload size successfully, the corresponding control signaling does not need to indicate the payload size again in the packet retransmission. That is, in the prior art, when the packet is transmitted initially and retransmitted, the control signaling needs to indicate both the RV and the payload size, and the RV indicated by the control signaling in the case of initially transmitting the packet and the payload size indicated by the control signaling in the case of retransmitting the packet are information not required to be indicated, which leads to waste of physical resources.